Role of auxin and its modulators in the adventitious rooting of Eucalyptus species differing in recalcitrance

Abstract

It is well established that auxins play a central role in the determination of rooting capacity, which is essential for vegetative propagation. Recent studies with apple trees have pointed to significant effects of auxin stability, wound related phenolics and ethylene production in the control of adventitious rooting. In the present study, a comparative analysis of the adventitious rooting of microcuttings of Eucalyptus saligna (easy-to-root species) and Eucalyptus globulus (difficult-to-root species) was carried out with different types of auxins, light intensities, presence or absence of apical meristem, different concentrations of phenolic compounds and presence or absence of an ethylene action inhibitor. Parameters evaluated were the percent rooting, number of roots per rooted cutting, length of longest root and mean rooting time. Results showed that auxins of intermediate stability are more favorable to rooting (particularly for the recalcitrant species), higher light intensities in the presence of exogenous auxins promote the rooting response, the absence of meristematic apex or externally supplied phenolics are not limiting for the rooting induced by exogenous auxins, and ethylene appears to play a minor role in the development of adventitious roots in microcuttings of Eucalyptus, indicating that the rhizogenic response results from direct effect of auxins.